1. Field of the Invention
This invention relates generally to trocars and other access devices which provide working channels into body cavities and form seals around instruments introduced into the working channel.
2. Discussion of the Prior Art
Trocars and other access devices are used to provide working channels across body walls and into body cavities, such as the abdominal cavity. A trocar typically includes an elongate tube or cannula which defines the working channel, and which is operatively inserted through the abdominal wall using an obturator. The obturator, with a sharp distal tip, is initially inserted into the working channel of the cannula. This combination is then pressed through the body wall at a puncture site. Finally, the obturator is removed leaving the cannula and its working channel to provide access into the body cavity.
The cavity is typically inflated to a pressure sufficient to enlarge the surgical environment. Maintenance of this inflation pressure is of particular importance to the procedure. With the cannula extending into the inflated cavity, the inflating gas would easily escape were it not for valves which extend across the working channel in a housing of the trocar. Both zero closure valves and septum valves are used for this purpose. These valves are configured to facilitate the introduction of instruments through the trocar while maintaining the inflation pressure by forming appropriate seals with the outer surface of each instrument.
An instrument is first inserted through a hole in a proximal wall of the trocar housing. Within the housing, the septum valve has typically been placed immediately distal of this proximal wall. The septum valve is highly elastomeric and commonly formed from latex which has an ability to stretch as much as 800% These elastomeric characteristics enable the valve to be used with many different instruments having highly variable outside diameters and surface configurations.
Insertion of these instruments through the proximal wall of the housing, the septum valve, zero closure valve, and the working channel has been addressed by many concepts in the prior art. However, it is the removal of the instruments which has been particularly difficult in some cases. When the instrument is removed, the septum valve initially attempts to invert. While this inversion can be tolerated in most instances, it becomes a severe problem if the instrument pulls the septum valve rearwardly where it can bind the instrument in the critical space which is formed between the proximal wall of the housing and the instrument.
This problem is most severe when the critical space is small, for example when the diameter of the instrument is only slightly smaller than the diameter of the hole. The problem is further compounded when the instrument is provided with a surface configuration which increases the coefficient of friction with the septum valve. Grit blasted finishes, which are commonly used to form anti-glare surfaces on instruments, are particularly detrimental to the removal process. Under these conditions, the septum valve has an even greater tendency to be pulled into the critical space. When these conditions exist together, it is often impossible to remove the instrument from the trocar as it is bound by an increasing pressure from the septum. Although the binding effect may be overcome by moving the instrument distally, additional attempts to remove it proximally merely re-create the problem. Under these conditions, it has been necessary to fully remove the entire trocar system in order to withdraw the instrument distally through the working channel. This is particularly aggravating to the surgeon who must then reinsert the trocar to provide the working channel access. Certainly if a surgeon knew that a particular instrument would bind upon removal, he would never insert it. But unfortunately, these circumstances are not easily predictable. Accordingly, the removal problem commonly occurs quite unexpectedly.